The Fraternal Birth-Order Effect as Statistical Artefact: Convergent Evidence from Probability Calculus, Simulated Data, and Multiverse Meta- Analysis

For a quarter of a century researchers investigating the origins of sexual orientation have largely ascribed to the fraternal birth order effect (FBOE) as a fact, holding that older brothers increase the odds of homosexual orientation among men through an immunoreactivity process. Here, we triangulate the empirical foundations of the FBOE from three distinct, informative perspectives: First, drawing on basic probability calculus, we deduce mathematically that the body of statistical evidence of the FBOE rests on the false assumptions that effects of family size should be controlled for and that this could be achieved through the use of ratio variables. Second, using a data-simulation approach, we demonstrate that by using ratio variables, researchers are bound to falsely declare corroborating evidence of an excess of older brothers at a rate of up to 100%, and that valid approaches attempting to quantify a potential excess of older brothers among homosexual men must control for the confounding effects of the number of older siblings. And third, we re-examine the empirical evidence of the FBOE by using a novel specification-curve and multiverse approach to meta-analysis. This yielded highly inconsistent and moreover similarly-sized effects across 64 male and 17 female samples (N = 2,778,998), compatible with an excess as well as with a lack of older brothers in both groups, thus, suggesting that almost no variation in the number of older brothers in men is attributable to sexual orientation.

Meiotic Drive in Chronic Lymphocytic Leukemia compared with other Malignant Blood Disorders

Studies of families with two or more cases of malignant blood disorders (lympoproliferative and/or myeloproliferative) provide a description of the pathway of susceptibility down through the generations towards the proband. The united observations fit into a non-Mendelian operational model consisting of parental genomic imprinting combined with feto-maternal microchimerism. Male affected relatives of a proband are predominant in paternal lines with maternal imprinting, while female affected relatives are predominant in lines with maternal affiliation and paternal imprinting. The findings suggest the influence of a so-called polymorphic equilibrium with segregation distortion related to parental imprinting (fitness optimalization). In the generations before a proband, affected relatives with the same diagnosis may covariate, viz. be present with a higher frequency than expected (relative superiority); or contravariate, that is a lower frequency than expected (mutual minority). Covariation has been observed especially among affected relatives with multiple myeloma, diffuse large B-cell lymphoma, acute myeloid leukemia, Hodgkin’s lymphoma and some few other diagnoses. Contravariation is only seen among affected relatives with chronic lymphocytic leukemia. The dynamic drive of susceptibility in an affected family with birth order effect and/or anticipation is regarded as an additional polymorphic equilibrium with segregation distortion caused by feto-maternal microchimerism.

Birth Order and Voter Turnout

Previous studies have stressed the role of a child's family environment for future political participation. This field of research has, however, overlooked that children within the same family have different experiences depending on their birth order. First-borns spend their first years of life without having to compete over their parents' attention and resources, while their younger siblings are born into potential rivalry. We examine differences in turnout depending on birth order, using unique population-wide individual level register data from Sweden and Norway that enables precise within-family estimates. We consistently find that higher birth order entails lower turnout, and that the turnout differential with respect to birth order is stronger when turnout is lower. The link between birth order and turnout holds when we use data from four other, non-Nordic countries. This birth order effect appears to be partly mediated by socio-economic position and attitudinal predispositions.

A method yielding comparable estimates of the fraternal birth order and female fecundity effects in male homosexuality

The fraternal birth order effect (FBOE) is the finding that older brothers increase the probability of homosexuality in later-born males, and the female fecundity effect (FFE) is the finding that the mothers of homosexual males produce more offspring than the mothers of heterosexual males. In a recent paper, Khovanova proposed a novel method for computing independent estimates of these effects on the same samples and expressing the magnitude and direction of the effects in the same metric. In her procedure, only families with one or two sons are examined, and daughters are ignored. The present study investigated the performance of Khovanova's method using archived data from 10 studies, comprising 14 samples totalling 5390 homosexual and heterosexual subjects. The effect estimate for the FBOE showed that an increase from zero older brothers to one older brother is associated with a 38% increase in the odds of homosexuality. By contrast, the effect estimate for the FFE showed that the increase from zero younger brothers to one younger brother is not associated with any increase in the odds of homosexuality. The former result supports the maternal immune hypothesis of male homosexuality; the latter result does not support the balancing selection hypothesis.

The relationship between Birth Order and Sales Person’s performance in Ghana.

AbstractsThe aim of the study is to predict the impact of birth order effect on sales person’s performance. The main objective is to investigate the relationship between birth order; (firstborns, middle children, lastborns, and only children) on sales person’s performance. Besides, it also aimed to examine the relationship between personality and sales person’s performance. The target population of the study comprised of sales person’s shared mean age of 21.0 years (Standard Deviation= 1.93) and have worked as sales person for a minimum of three years. Participants were recruited from the Greater Accra Region of Ghana. The study adopted purposive sampling technique to select the sales person and a total of 788 out of the 900 participants returned their questionnaires. A linear regression equation was employed to measure how birth order predicts sales person’s performance, with birth order (firstborns, middle children, lastborns, and only children) as the predictor variables and sales person’s performance as the criterion variable. Results indicated that a participant of different birth positions does not differ significantly in terms of sales person’s performance.Keywords; Birth Order; sales person’s Performance; firstborn; Extraversion; Middle children

First come, first served? Birth order effects on child height in South Africa

We examine the birth order effects on health status for a sample of children aged 1–18 years in South Africa. Using a mother fixed-effects specification, we observe children's height-for-age z-score decreases with birth order. We investigate potential mechanisms underlying the birth order effect including those related to biology, parental preferences, and resource dilution. We also look at whether these effects are due to selection into families of different sizes. We find that the magnitude of the effect is larger in poorer and rural households and in larger families – suggesting that the birth order effect is largely due to resource dilution in economically constrained households.